The present invention relates to a method and a device for acquiring data, in particular, for acquiring the minimum value or the maximum value of a multiplicity of measured values which are present at a multiplicity of measuring points.
A conventional method for generating such a maximum value or minimum value addresses in succession measuring points which are connected by means of a bus or the like to a control unit, for example, a micro-processor, in order to cause them to output their measured value to the control unit and subsequently determine, at the control unit, the maximum value or minimum value of the measured values. Such a method is technically complex as each individual measuring point has to have an interface which is capable of detecting when the respective measuring point is addressed by the control unit, and this interface gives rise to a considerable amount of data traffic on the bus on which the requests to the measuring points to supply a measured value and their responses have to be successively transmitted. A particularly high loading results if a packet-oriented bus has to be used, for example, because it is necessary to connect not only the measuring points but also data units which transmit or receive large quantities of data in a short time.
WO 00/68700 discloses a method and a device for deriving a maximum value or a minimum value from measured values which are generated at a multiplicity of measuring points, in which method and device the measuring points are not located in parallel on a bus and addressed by one control unit but rather connected in series along a data line so that each measuring point can receive data in each case from only one preceding point arranged upstream on the data line, compare it with its own measured value and pass on the respective larger value or smaller value to a succeeding point. In such an arrangement the need to address each measuring point individually is eliminated so that the individual measuring points also do not require an address decoder and can thus be simplified. The period of time which is necessary to acquire a maximum value or minimum value is however extremely long as the measuring points which are connected serially to one another each have to receive a data value completely from a preceding point before they carry out the comparison with their own measured value and pass on the value which is selected from the two values.
It would also be possible to reduce these delays by providing a parallel transmission of the data values between adjacent measuring points, but such a solution is complex and costly, in particular if the measuring points are used in an environment in which electromagnetic interference is frequent, and it is therefore necessary to shield the data line.